Help with Synology NAS across two sites

We have two Synology NAS sites. Location A has media loaded onto it (video, audio, presentations) and Location B is an offsite backup, where we want a one-way load of content at all times. We need help setting up DDNS so that the sync is fast and secure. After this is working and the sync is complete, we would also like help with PLEX on the first NAS.